The present invention relates to improvements in scanning interference electron microscopy for evaluating the magnetic property of micro-areas in magnetic materials. More particularly, the invention relates to a scanning interference electron microscope which operates on a novel signal detection method for higher detection sensitivity and which is functionally enhanced to analyze ever smaller parts of the sample.
In recent years, various attempts have been made to evaluate the magnetic property of micro-areas in magnetic materials through the use of electron microscopes. Two kinds of electron microscopes have been primarily used in such cases: holography electron microscopes, and scanning transmission electron microscopes that utilize phase difference contrast. A typical holography electron microscope is described in "PHYSICAL REVIEW B," Vol. 25, No. 11, pages 6799-6804 (June 1982). This holography electron microscope operates as follows: A primary electron beam is irradiated onto a wide area covering the inside as well as the outside of a sample. Part of the electron beam is transmitted inside the sample, and part thereof is allowed to pass outside the sample. An electron biprism causes the two electron beam parts to interfere with each other, generating interference fringes. A position difference of the interference fringes is then detected. This difference represents a phase difference of the electron beam as it interacts with the sample while passing therethrough. Because the phase difference is particularly pronounced in response to magnetic field changes, the holography microscope can evaluate with high sensitivity the magnetic property of micro-areas in the magnetic sample under observation.
Meanwhile, a typical scanning transmission electron microscope is discussed in "JOURNAL OF APPLIED PHYSICS," Vol. 64, No. 10, pages 6011-6013 (Nov. 1988). This electron microscope works as follows: A primary electron beam is irradiated and focused on the surface of a sample. An electron beam deflection system causes the irradiated spot of the electron beam to scan the sample surface, generating what is known as a scanning transmission electron microscopic image. Viewing the image, the observer determines on the sample surface a point to be evaluated. When the primary electron beam is irradiated onto that point, the Lorentz force arising from the magnetic field within the sample deflects the beam. The deflection angle of the electron beam is then measured. The measurements permit evaluation of the magnetic property of micro-areas in the sample being observed. Since the primary electron beam is focused when irradiated onto the sample, an electron diffraction pattern and fluorescent X-rays are also detected from the irradiated spot of the beam on the sample surface. These findings allow micro-areas in the sample to be evaluated in terms of crystalline quality and element composition concurrently with magnetic property observation.
Although conventional electron microscopes provide, as described, effective means for evaluating the magnetic property of micro-areas in magnetic materials, they have some conspicuous disadvantages. One disadvantage of the holography electron microscope is that the crystalline property and element composition of micro-areas in the sample cannot be evaluated concurrently with the magnetic property thereof. This is because the primary electron beam of the holography electron microscope is not focused but expanded over a wide area of the sample surface. On the other hand, one disadvantage of the scanning transmission electron microscope based on phase difference contrast is its poor capability to precisely measure magnetic fields with high sensitivity. The reason for this is that, with the scanning transmission electron microscope, the angle of deflection of the primary electron beam caused by the Lorentz force from the magnetic field within the sample is as small as 10.sup.-4 to 10.sup.-5 rad.